One of the problems arising when tweaking or adjusting the quantizer
tables is that there are a lot of look up tables that depend on the QINDEX.
Any adjustment to the link between QINDEX and real quantizer therefore tends
to break aspects of for example the rate control.

In this check in I have replaced several of the look up tables with functions that
approximate the same results as the old Q luts but use a formulaic approach
based on real Q values rather than QIndex. This should hopefully make it easier
to experiment with changes to the Q tables without always having to go through
and hand optimize a set of look up tables. Once things stabilize we may choose
to re-instate luts for the sake of performance.

Patch 2:
    Addressed Ronald's comments.
    vp8_init_me_luts() Added so luts only initialized once.

Change-Id: Ic80db2212d2fd01e08e8cb5c7dca1fda1102be57